For the heterogeneous catalytic reaction using a solid catalyst of pellet or spherical shape, a fixed bed reactor or a multi-tube type reactor functioning as a heat exchanger is generally used. The multi-tube type reactor is in particular used for a reaction generating a very large reaction heat and showing a remarkable increase of catalyst temperature (see, for example, JP-A-2001-139499 and JP-A-2001-137689).
These publications disclose, as examples of reaction, the production of an ethylene oxide from ethylene and oxygen, the production of acrolein or an acrylic acid by the oxidation of propylene, the production of methacrolein or a methacrylic acid by the oxidation of isobutylene or tertiary butanol, the production of formalin from methanol and so on.
The catalyst used for these reactions is generally in a spherical or cylindrical shape having a diameter of from 2 to 15 mmΦ, and the reaction tubes of the multi-tube type reactor are generally in a cylindrical shape having an inner diameter of from 20 to 50 mmΦ and a length of from 1 to 5 m. For an industrial purpose, a single reactor has reaction tubes in a number of from several thousands to several ten thousands.
In order to cool or heat the reaction tubes, a heat transfer medium is circulated in a space (at a shell side) defined by the shell (outer shell) of the reactor, surrounding the reaction tubes and a tube plate for fixing the reaction tubes, and a part of the heat transfer medium is discharged and is cooled or heated to be returned repeatedly to the reactor.
As the heat transfer medium, a molten salt such as a nitrate mixture, an organic heat transfer medium containing as the major component a polynuclear aromatic compound, boiled water or a boiled organic medium is generally used.
As an example of a reaction in which absorption of heat in the reaction decreases the temperature of a starting material gas whereby the progress of the reaction is delayed or the ultimate reaction rate decreases, there is known the production of styrene by the dehydrogenation of ethyl benzene.
Conventionally, a fixed bed reactor has been used for such reaction in which a reaction heat is supplied to a starting material gas by supplying a preheated hot gas. A multi-tube type reactor is sometimes used. However, there is restriction on the heat transfer medium to be supplied to the shell side because it is necessary to elevate the temperature to around 600° C.
Such conventional multi-tube type reactor has cylindrical reaction tubes in a number of from several thousands to several ten thousands and a solid catalyst of pellet or spherical shape filled in the reaction tubes, and the control of temperature to the catalyst layer is carried out by supplying a heat transfer medium into the shell at an outer side of the reaction tubes and adjusting the temperature of the heat transfer medium.
When a heterogeneous gas phase reaction is carried out in the multi-tube type reactor, the reaction region in a part of ⅓ from the inlet for a starting material gas in the all reaction regions in the reaction tubes indicates the largest reactivity. FIG. 7 shows the temperature profile in the catalyst layer.
However, the surface area of heat transfer for removing the reaction heat is equal in the all reaction regions because it depends on the outer surface area of the reaction tubes. Further, the temperature at the shell side to which the heat transfer medium was introduced was contrived to have a uniform temperature as possible, and the supply of the heat transfer medium and the flow pattern of it were contrived so as to keep the same medium temperature on a plane perpendicular to the reaction tubes whereby reactions occurred at the same temperature in the almost reaction tubes. Accordingly, with respect to the removal of reaction heat or the application of heat over the all reaction regions, the reaction regions of the reaction tubes are according to the same design.
However, the temperature profile in a catalyst layer in a reaction tube is such that in the reaction region in the vicinity of the inlet of reaction tube where the reactivity is large, the removal of heat generated by the reaction is insufficient and the heat is accumulated in the catalyst layer to elevate the temperature of the catalyst layer. In the extreme case, the catalyst is damaged due to a high temperature. This phenomenon is called “a hot spot”.
In a case of oxidation reaction accompanying an extremely large heat, there was the problem that the temperature of the catalyst layer was very high in, in particular, the reaction region in the vicinity of the catalyst layer inlet, hence, a hot spot being easily formed. The hot spot in the catalyst layer elevates the temperature at the surface of the catalyst to accelerate the deterioration of the catalyst in this reaction region and reduces the selectivity of reaction, whereby the yield of the product decreased.
In order to avoid the hot spot, an improving method such that temperature profiles in catalyst layers in reaction tubes are equalized, has conventionally been proposed. For example, as a method for obtaining a good reaction performance and a high yield, there is proposed an improvement that a plurality of inlets are provided for a heat transfer medium supplied to the shell side of the reactor, and the heat transfer medium is supplied with different temperatures so that the heat transfer medium is controlled to have different temperatures at positions along the axial direction of the reaction tubes.
In order to supply the heat transfer medium having different temperatures from different positions of the reaction tubes, however, it is necessary to provide the same number of heat transfer medium supply equipments as the different temperatures on the heat transfer medium. Further, it is difficult to mix quickly at the shell side the supplied heat transfer medium having different temperatures with the heat transfer medium circulated in the reactor. This brings further non-uniformity of the heat transfer medium temperature at the shell side of the reactor.
On the other hand, there is a method that plural kinds of catalysts are filled in a reaction tube or a catalyst is mixed with an inert dilution agent so as to control the reactivity in the reaction region at the inlet.
This method is to control the temperature of the catalyst layer by controlling the reaction heat generated in or drawn from the reaction region in the vicinity of the inlet. However, in the case of using an industrial reactor having reaction tubes in a number of several thousands to several ten thousands, plural kinds of catalysts have to be uniformly filled in reaction regions of reaction tubes while adjusting the activity of the catalysts, or in using a dilution agent, mixtures of plural kinds of catalysts and the dilution agent have to be uniformly filled in the reaction tubes. When the catalysts in the reaction tube are to be replaced by new ones, much labor and a long time are needed to replace the catalysts. During the replacement the reaction has to be stopped.
Further, when the activity of reaction has to be adjusted by using a catalyst having a low reaction activity or by diluting a catalyst with an inert material, a larger amount of catalyst than originally intended has to be filled in reaction tubes, or an inert material which is basically unnecessary has to be filled in reaction regions. This caused a large pressure loss in a starting material gas passed through the catalyst layer. In particular, in an oxidation reaction, there was the problem of increasing power for a blower or a compressor necessary to compress molecular oxygen-containing gas such as air.
It is an object of the present invention to provide a new plate type catalytic reactor in which a temperature increase in a catalyst layer can be suppressed to prevent the formation of a hot spot and to prevent the deterioration of the catalyst filled in the catalyst layer whereby the service life of the catalyst can be prolonged; the optimum selectivity of reaction is attainable, and a pressure loss increase in a starting material gas passed through the catalyst layer can be prevented, in employing a heterogeneous gas phase reaction method using a solid catalyst of pellet or spherical shape.